PHP Script to Allow Site Visitors to Grant Access to their Google Analytics Data

I'm a web developer looking for some assistant with pulling data from Google Analytics. I can do this for my own accounts but want visitors to the website to be able to authorise my website to access their Google Analytics data. I can do this if I ask them for their username, password and profile ID but obviously I don't want to do this. I instead want to to use the OAUTH system to have access granted via a token/key. Ideally the access granted should be ONLY to the Google Analytics data and it should be Read Only. I'll also need a simple function created to illustrating how to run a GAPI query in PHP to return the data from Google Analytics. It may be easier to use Javascript OAUTH to get the access granted - this is fine, I just need a reliable way to get the token/key stored in a database to pull data in the future. It doesn't need to be pretty - just a collection of files that does what I've asked - I can do the rest! :-D